Subjective daily wear performance of two silicone hydrogel lenses

Silicone hydrogel lenses were introduced in Europe in 1999. The first two products: PureVision (Bausch and Lomb) and Night & Day (Ciba Vision) were launched with a recommended wearing regime of 30 nights' continuous wear. This indication was driven by the high oxygen flux that both products have; each providing 98-99 per cent of the oxygen that would be available to the cornea with no lens wear for the open eye.1,2
Although both products soon took the major share of extended wear fits, the extended wear market was slow to establish, with both lenses representing less than 2 per cent of new fits in the UK in 2004 and 7.5 per cent of contact lens sales.3
A factor holding back the wider adoption of first-generation silicone hydrogels was the relatively high modulus of the materials, resulting in some levels of discomfort and signs of corneal trauma such as superior epithelial arcuate lesions (SEALs).4 Concern also persisted over extended wear. While recent research suggests silicone hydrogels might reduce the incidence of adverse reactions in extended wear compared to conventional hydrogel extended wear,5 the same research supports that of others over the years that shows daily wear of contact lenses results in fewer adverse reactions.6-8 These factors contributed to the increasing use of these first-generation silicone hydrogel lenses as daily wear products.
In 2004 two new silicone hydrogels were launched: Acuvue Advance with Hydraclear (Johnson & Johnson Vision Care) and O2Optix (Ciba Vision). Both lenses are primarily intended for daily wear, although O2Optix also has an extended wear indication. Acuvue Advance is recommended for two-weekly replacement; O2Optix is recommended for monthly replacement in Europe although in the US the recommendation is for two-weekly replacement (Table 1).
Although some clinical data has been published on the products individually,9-11 to date no data has been published on the comparative performance of the lenses. This paper will report on the short-term subjective response.
Both lenses rely on a silicone hydrogel polymer backbone to deliver high oxygen levels to the eye; both provide the eye with 97-98 per cent of the oxygen that would be available if no lens was worn at all in the open eye situation (Figure 1). The moduli of both lenses are significantly lower than the first-generation silicone hydrogels (Figure 2), Acuvue Advance having a modulus similar to traditional hydrogel lenses.9
Wettability is achieved by a plasma surface treatment with the O2Optix, and by Hydraclear patented technology with Acuvue Advance, combining the lens material with a moisture rich wetting agent.

Method
A multi-centre, bilateral, monadic (parallel), sponsor-masked study was carried out to compare subjective responses to Acuvue Advance and O2Optix over two weeks of lens wear.
The monadic study design provides one of the toughest ways of showing a difference between two products, but is one of the most accurate means of reflecting real-world product performance across multiple categories.
The monadic study relies on a number of larger groups of subjects experiencing only one of a number of products and rating its performance in absolute terms against any previous category experience. When differences in performance are seen with this methodology there is a high likelihood that they will be reflected in the market. Whereas a cross-over study, where the subjects experience both products, tends to magnify small differences in subjective variables. In addition, the experience of the products is separated by time.
A total of 26 eye care practitioners were recruited by an independent research company, representing a mix of independent and retail practices across the US. The practitioners had between two and 29 years' experience. These practitioners recruited current daily wear soft spherical contact lens wearers, with a spherical prescription between -1.00 and -6.00DS with <1.00DC of astigmatism. The gender, age and ethnicity of subjects were representative of the marketplace. A total of 337 subjects were assigned to one of two groups, each assigned to wear just one of the products to be evaluated. Differences in subjective responses were tested at 95 per cent significance level.
All variables were assessed on a five-point scale, a typical rating being a choice from 'excellent', 'very good', 'average', 'poor' and 'very poor'. This report will look at the percentage of 'top two box' responses ('excellent' or 'very good') by patients. Subjective assessments using a questionnaire were made at the initial visit, and after one and two weeks.

SUBJECTIVE RESULTS (one WEEK)
Vision
Three-quarters of Acuvue Advance patients rated overall vision quality as 'excellent' or 'very good', which was statistically significantly higher than the 66 per cent of O2Optix patients with top two box ratings. Breaking the assessment of vision down into individual attributes (Figure 3), Acuvue Advance showed significantly higher top two box scores for all key variables at the 95 per cent confidence level.

Comfort
Acuvue Advance was rated as having better overall comfort to O2Optix (71 per cent vs 59 per cent, p<0.05). Comfort was higher at initial insertion (77 per cent vs 68 per cent, p<0.05), and remained higher as the day wore on with 51 per cent rating end-of-day comfort on top two box with Acuvue Advance versus 37 per cent for O2Optix (p<0.05).
Some 81 per cent of Acuvue Advance patients reported top two box scores for being able to wear the lenses comfortably for more than nine hours against 71 per cent reporting the same for O2Optix (p<0.05). Differences in comfort between the two products were also seen across a series of broader attributes relating to comfort (Figure 4).

Handling
There was no significant difference in the top two box rating of overall handling between the lenses, although Acuvue Advance had a higher top two box score for ease of removal (75 per cent vs 65 per cent p<0.05).

Overall satisfaction
Acuvue Advance had a significantly higher overall rating than O2Optix (67 per cent vs 54 per cent, p<0.05). 69 per cent of the Acuvue Advance group stated they would 'definitely' or 'probably' buy the lens, which was significantly higher than the 54 per cent of the O2Optix group against the same measure.
If satisfaction drives recommendations then it was not surprising to see that a higher proportion of the Acuvue Advance group would recommend the lens to others than the O2Optix wearers (77 per cent versus 67 per cent, p < 0.05).
Finally, although not one of the key variables within the current report, the high levels of satisfaction among wearers of Acuvue Advance were also reflected by the prescribing eye care practitioners with 72 per cent having a top two box rating for the product versus 60 per cent of the practitioners that prescribed O2Optix.

DISCUSSION
For any contact lens to be successful it has to deliver on three key attributes; comfort, vision and health. Patients comment on their subjective response to the variables of lens comfort and vision and in many cases these are the variables used to select the prescribed product. Silicone hydrogels are known to deliver 95 per cent or more available oxygen to the cornea and are therefore able to benefit ocular health.

Vision
The basic requirement of all contact lenses is that the patient can see clearly through them. Although all patients were prescribed the appropriate prescription to optimise their visual acuity, there were significant differences in the subjective vision responses between the two test lenses. Subjective visual assessment is the result of multiple factors and the literature has long established the lack of a direct correlation between visual acuity and self reported visual quality.12 Reliability and repeatability in manufacture and good stability of the pre-lens tear film may well be contributory to the apparent visual benefit of Acuvue Advance.

Comfort
The comfort responses appear to show benefits for the use of Hydraclear patented technology. In every variable of comfort assessed, Acuvue Advance was rated as better satisfying the comfort needs of patients than O2Optix. These differences became more pronounced as the day progressed.
The higher all day comfort of Acuvue Advance is most evident in the questions concerning how long the patients were able to wear the two lenses comfortably. In practice it is easy to get simple responses to the questions: 'Are your lenses comfortable?' and 'How long do you wear your lenses each day?' but neither of these questions is sufficient to get at a truer picture of a patient's satisfaction with lenses. In the former case, the answer is always going to be given within the paradigm of the patient's definition of comfort.
Many contact lens wearers accept that there is some discomfort with contact lenses based on the experience of lens wearers over many years. It is only when the question is expanded, for example: 'How do your lenses feel towards the end of the day?' that a much more relevant picture of how the patient is getting on with their lenses is reached.
Perhaps the most pertinent question might be, 'How long can you wear your lenses comfortably?' This might show up any issues with discomfort. This study suggests how many more wearers were able to comfortably wear Acuvue Advance with Hydraclear for more than nine hours than O2Optix.

Overall satisfaction
The comparatively higher levels of overall satisfaction reported with Acuvue Advance are consistent with the preference reported in vision and comfort. A recent Harvard Business School paper13 proposed that the single most important question to gauge satisfaction
across multiple service and product categories was to see if a user would recommend the product to somebody else. In this context, the Acuvue Advance performed well.

Conclusions
This controlled study is the first to report data across two large groups of patients showing consistently better subjective responses for Acuvue Advance than for O2Optix. In most variables tested the Acuvue lens was rated higher at the 95 per cent level.
The study has also pointed the way towards a broader series of questions that can help the contact lens practitioner identify issues of concern to their patients. By delving into these unmet needs we should be able to satisfy more current contact lens wearers and bring more lapsed wearers back to lenses.
With Hydraclear patented technology soon to be launched in a toric lens these authors believe that there is a new alternative for the first time contact lens wearer as well as a product to improve the overall satisfaction for existing contact lens patients.

Acknowledgements
To our global colleagues who designed and managed this comprehensive patient satisfaction study.

References
A full list of references is available from the clinical editor. Email: william.harvey@rbi.co.uk

Ian Davies is vice president, new business opportunities & professional affairs. Jane Veys is director, clinical affairs at Johnson & Johnson Vision Care, Europe, Middle East & Africa